String alignment question
05-22-2020, 09:46 PM
#1
Pro
Thread Starter
String alignment question
I've done so much research on this and have done string alignments with good success in the past but I want to be sure I'm doing it properly on my 911.
When a fellow racer tells you something like, "you want 6mm of total rear toe-in", is that as measured from the tire's road contact surface or from the edges of the wheel? I've always measured from the wheel, but given that the tire is of greater diameter, there will be a different reading if taken from the tire.
I understand this is why it's better to use degrees instead of linear measurements, but most racers and performance articles give it in linear measurement.
There appears to be as many people saying to measure from the tire as there are from the wheel, in google searching. Tires move and flex and it can be difficult to find a consistent place to measure from so I'd rather use the wheel. I just want to know if the alignment values people throw out there are meant to be taken at the wheel or the tire (the latter case would mean taking them from the wheel and using math to determine actual value from the tire).
Thanks in advance.
When a fellow racer tells you something like, "you want 6mm of total rear toe-in", is that as measured from the tire's road contact surface or from the edges of the wheel? I've always measured from the wheel, but given that the tire is of greater diameter, there will be a different reading if taken from the tire.
I understand this is why it's better to use degrees instead of linear measurements, but most racers and performance articles give it in linear measurement.
There appears to be as many people saying to measure from the tire as there are from the wheel, in google searching. Tires move and flex and it can be difficult to find a consistent place to measure from so I'd rather use the wheel. I just want to know if the alignment values people throw out there are meant to be taken at the wheel or the tire (the latter case would mean taking them from the wheel and using math to determine actual value from the tire).
Thanks in advance.
05-22-2020, 10:11 PM
#2
Tires flex. Use the wheels for a more true measure ( unless wheels are bent).
I've done the strings and setting it up was.a pain (very time consuming). If you search for diy alignment hubs, you'll find an interesting solution to your problem. With these hubs you can also easily corner balance assuming you got scales. The cost of the hubs is easily offset by the time you save.
you may also want to read up on thrust angle.
I've done the strings and setting it up was.a pain (very time consuming). If you search for diy alignment hubs, you'll find an interesting solution to your problem. With these hubs you can also easily corner balance assuming you got scales. The cost of the hubs is easily offset by the time you save.
you may also want to read up on thrust angle.
05-22-2020, 11:20 PM
#3
Rennlist Member
Thrust angle sounds so dirty.
Use the wheels. Absolutely check for runout - if your reference points are out by even a mm then that's a big margin of error when setting rear toe at 2mm per side.
If you want to do some basic trig you can compensate for a 15, 16, 17, 18, 19" (you get the idea) wheel diameter when measuring for "2mm" of toe-in. But if there's still rubber in the suspension and using street tires then this kind of precision measurement adjustment probably isn't worth it IMHO.
Lastly, remember that rake matters (particularly in a 911) and is an integral part of alignment that is often underappreciated.
Use the wheels. Absolutely check for runout - if your reference points are out by even a mm then that's a big margin of error when setting rear toe at 2mm per side.
If you want to do some basic trig you can compensate for a 15, 16, 17, 18, 19" (you get the idea) wheel diameter when measuring for "2mm" of toe-in. But if there's still rubber in the suspension and using street tires then this kind of precision measurement adjustment probably isn't worth it IMHO.
Lastly, remember that rake matters (particularly in a 911) and is an integral part of alignment that is often underappreciated.
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Hindsight2010 (05-25-2020)
05-23-2020, 12:15 AM
#5
Three Wheelin'
Nobody measures from the tires, so measurements people talk about assume you are measuring at the wheel.
Another thing - make sure you are measuring our car on a flat surface. Most surfaces (like garages) that look flat are usually not just slanted, but wavy, so would cause different suspension heights at each corner of the car (which will affect toe). You can check with a good level, and use cheap vinyl tiles from Home Depot are good for shimming the corners that need to be raised.
Another thing - make sure you are measuring our car on a flat surface. Most surfaces (like garages) that look flat are usually not just slanted, but wavy, so would cause different suspension heights at each corner of the car (which will affect toe). You can check with a good level, and use cheap vinyl tiles from Home Depot are good for shimming the corners that need to be raised.
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Hindsight2010 (05-25-2020)
05-23-2020, 12:36 AM
#6
Three Wheelin'
I have found the Puhn book and the SmartStrings instructions excellent resources when teaching someone how to string. The developer of SmartStrings is a friend-- longtime PCA member and local racer. He went on to do racing engineering work for Flying Lizards Motorsports for many years and had great success along with that team. SmartStrings instructions in particular are a great reference resource. And the product is great as well... I got to check in with him during the design phase years ago.
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Hindsight2010 (05-25-2020)
05-25-2020, 11:40 AM
#7
Pro
Thread Starter
Thanks everyone for the replies!
Yeah I have been planning this. Hard to know how much rake I *should* have, for a performance alignment. I have no aero (car is a 997.2 C2S) so my plan is to measure and preserve the factory rake setting, while lowering the car front and rear.
Got it thank you! That makes it so much easier. As for the flat surface, I 100% agree. I measured my driveway and my garage using a laser-beam level and found it to be up and down all over the place, by as much as 2 inches. I would love to buy some leveling plates (the kind with threaded adjustable leveling feet) but all are extremely expensive. I can weld, so thought about fabricating my own, but it would take a long time to fabricate and heavy duty leveling feet are shockingly expensive. So I settled on building some over-engineered plywood platforms that are about 12" high. I will use a combination of smooth hardwood plywood shims and plexiglass shims to get the level perfect on all four corners with my laser beam level, while giving me the room I need to crawl under the car to make the adjustments. I plan to make them long enough that I can roll the car forward and backward a bit in order to help unload the suspension between adjustments.
Thanks - yeah I finally bit the bullet and bought the smart strings setup last week. $450 is a lot to pay for what you get but if it saves me hours of setup time and increases accuracy vs the home-brewed kit I was using, I think that's a fair trade. I agree their docs are great, and the have been very helpful in e-mailed support as well.
Last question: Anyone have any input on alignment specs? I drive the car about 3,000 miles a year. I plan to track it at HPDE days at least once a month. It isn't my daily. I'm currently going for:
Thanks again!
Nobody measures from the tires, so measurements people talk about assume you are measuring at the wheel.
Another thing - make sure you are measuring our car on a flat surface. Most surfaces (like garages) that look flat are usually not just slanted, but wavy, so would cause different suspension heights at each corner of the car (which will affect toe). You can check with a good level, and use cheap vinyl tiles from Home Depot are good for shimming the corners that need to be raised.
Another thing - make sure you are measuring our car on a flat surface. Most surfaces (like garages) that look flat are usually not just slanted, but wavy, so would cause different suspension heights at each corner of the car (which will affect toe). You can check with a good level, and use cheap vinyl tiles from Home Depot are good for shimming the corners that need to be raised.
I have found the Puhn book and the SmartStrings instructions excellent resources when teaching someone how to string. The developer of SmartStrings is a friend-- longtime PCA member and local racer. He went on to do racing engineering work for Flying Lizards Motorsports for many years and had great success along with that team. SmartStrings instructions in particular are a great reference resource. And the product is great as well... I got to check in with him during the design phase years ago.
Last question: Anyone have any input on alignment specs? I drive the car about 3,000 miles a year. I plan to track it at HPDE days at least once a month. It isn't my daily. I'm currently going for:
- As much caster as I can get using the GT3 LCAs up front
- 0 front toe
- 5-6mm rear toe-in
- -2.5 front camber
- -2.25 rear camber
Thanks again!
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05-25-2020, 01:32 PM
#8
Three Wheelin'
You do not need to be on a level surface to measure and adjust toe. Craig Watkins invented SmartStrings and still sells the kit. His team, the Flying Lizards ran water-cooleds and won many professional sports car races. I often saw them using SmartStrings in the paddock. He knows his stuff. And he is a PCA member, Club racer and vintage racer as well.
I do not own a SmartsStrings toolset-- I made a custom set up that attaches directly to my car for about $30. Easy for a race care with removable fiberglass panels.
- Mike
I do not own a SmartsStrings toolset-- I made a custom set up that attaches directly to my car for about $30. Easy for a race care with removable fiberglass panels.
- Mike
05-25-2020, 02:11 PM
#10
Rennlist Member
So an eyeball "flat" surface is fine for toe.
If you're going to preserve factory rake, good trick is to measure it with a digital inclinometer on a reference surface (rocker, door plate, etc). You may want to adjust rake a bit beyond that to fine tune handling balance.
If you're going to lower the car then consider bump adjustment, particularly if you have aftermarket rear toe links that allow for shimming.
Lastly 6mm of total rear toe-in is a lot, particularly with zero toe in the front. The car is going to resist turning
Consider starting with 4mm total toe-in and see how it goes from there.
Do you have a diff? All setup decisions should start there.
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Hindsight2010 (05-25-2020)
05-25-2020, 02:21 PM
#11
Pro
Thread Starter
You need a fair amount of droop or compression to get out of the reasonable sweet spot on the bump curve.
So an eyeball "flat" surface is fine for toe.
If you're going to preserve factory rake, good trick is to measure it with a digital inclinometer on a reference surface (rocker, door plate, etc). You may want to adjust rake a bit beyond that to fine tune handling balance.
If you're going to lower the car then consider bump adjustment, particularly if you have aftermarket rear toe links that allow for shimming.
Lastly 6mm of total rear toe-in is a lot, particularly with zero toe in the front. The car is going to resist turning
Consider starting with 4mm total toe-in and see how it goes from there.
Do you have a diff? All setup decisions should start there.
So an eyeball "flat" surface is fine for toe.
If you're going to preserve factory rake, good trick is to measure it with a digital inclinometer on a reference surface (rocker, door plate, etc). You may want to adjust rake a bit beyond that to fine tune handling balance.
If you're going to lower the car then consider bump adjustment, particularly if you have aftermarket rear toe links that allow for shimming.
Lastly 6mm of total rear toe-in is a lot, particularly with zero toe in the front. The car is going to resist turning
Consider starting with 4mm total toe-in and see how it goes from there.
Do you have a diff? All setup decisions should start there.
Yes, I do have aftermarket rear toe links that are of the shimmable variety for bump-steer adjustment. I also have a digital bump-steer gauge which I plan to use to get the shims right. I've only worked on bump steer with one other vehicle, but I did it front and rear since both were adjustable on that car, so I learned a lot about it in the process.
Thanks for the rear toe input. I was going with 5-6 as that is what a guy at Tarett advised me to try. But maybe I will start with 4 and go up and down a bit to see how it changes things.
Diff? If you are referring to a limited slip differential, not to my knowledge. I don't think the 997.2 C2S has one and I have not added one to the transaxle.
05-25-2020, 06:04 PM
#12
Three Wheelin'
"Doesn't toe change through the range of suspension travel? If so, having a non-level surface would impact the toe readings."
Think about it... you are setting toe with the car at a static height. No suspension load other than the car, or the car plus driver ballast. So no-load = no impact on toe setting. You just need to think about it.
I do the full monty set up on my race cae, camber, caster and toe. Have been doing so for 25+ years. I have also done set up on the cars of numerous friends. Trailing arm 911 cars can be a pain, but I have some techniques and tricks I use. Like many, I measure toe in inches. Typically and eighth inch or so total toe out up front, and a sixteenth inch of total toe in out back. These are really common settings. I even used them on my 944/951 family cars back in the day.
Level ground is not important, BUT it is critical to ensure that your suspension is fully settled on the ground. Even with all racing parts (no rubber; solid mounts and bearings throughout) this is critical. In a pinch I have used large garbage bags in all four corners, with WD40 or similar sprayed between layers for "slip." On my set up platform, I use some thing plastic sheets with white lithium grease sprayed between.
When I first started doing set up around 1994, I was given some advice from Jeff and David Stone at Kelly Moss. They suggested cookie sheets, but I found plastic more to my liking.
Of course you are right tht toe changes with ride height, so with suspension load changes you get toe change. And potential bump steer front and/or rear.
I strongly suggest the Puhn book as a reference.
I have my own scales (bought a once used set of $1k Longacres via a Craigslist ad and at a steep discount 5-6 years ago), and some leveling platforms via E-Bay.
My SmartCamber tool was assembled in 1997 or so from a $50 digital level module and a blem frame I got from SmartRacing Products.
And by the way, I have found Tarett to be a great provider of parts. I know Ira and i know he has learned a lot through the years, including obtaining valuable perspective from set up guru Cary Eisenlohr.
Good luck.
Think about it... you are setting toe with the car at a static height. No suspension load other than the car, or the car plus driver ballast. So no-load = no impact on toe setting. You just need to think about it.
I do the full monty set up on my race cae, camber, caster and toe. Have been doing so for 25+ years. I have also done set up on the cars of numerous friends. Trailing arm 911 cars can be a pain, but I have some techniques and tricks I use. Like many, I measure toe in inches. Typically and eighth inch or so total toe out up front, and a sixteenth inch of total toe in out back. These are really common settings. I even used them on my 944/951 family cars back in the day.
Level ground is not important, BUT it is critical to ensure that your suspension is fully settled on the ground. Even with all racing parts (no rubber; solid mounts and bearings throughout) this is critical. In a pinch I have used large garbage bags in all four corners, with WD40 or similar sprayed between layers for "slip." On my set up platform, I use some thing plastic sheets with white lithium grease sprayed between.
When I first started doing set up around 1994, I was given some advice from Jeff and David Stone at Kelly Moss. They suggested cookie sheets, but I found plastic more to my liking.
Of course you are right tht toe changes with ride height, so with suspension load changes you get toe change. And potential bump steer front and/or rear.
I strongly suggest the Puhn book as a reference.
I have my own scales (bought a once used set of $1k Longacres via a Craigslist ad and at a steep discount 5-6 years ago), and some leveling platforms via E-Bay.
My SmartCamber tool was assembled in 1997 or so from a $50 digital level module and a blem frame I got from SmartRacing Products.
And by the way, I have found Tarett to be a great provider of parts. I know Ira and i know he has learned a lot through the years, including obtaining valuable perspective from set up guru Cary Eisenlohr.
Good luck.
05-26-2020, 09:02 AM
#14
Three Wheelin'
Can you measure toe on a non-level surface? Sure. There is definitely less impact of a non-level surface on toe than on other measurements like camber. As noted, just eyeing a surface can easily yield inches worth of being non-level. In my mind, for quick and dirty measurement, that may well be good enough. If you're someone who doesn't plan on checking toe that often, I figure once you're taking the time to measure toe, you might as well take a little extra time and set a flat surface for measuring it. Up to individual preference.
05-26-2020, 11:53 AM
#15
Three Wheelin'
"Level is necessary if you want repeatability."
Sorry, this is just not true. It isn't "necessary"-- repeatability can be achieved without a level surface.
Think about it.
Again:
"Doesn't toe change through the range of suspension travel? If so, having a non-level surface would impact the toe readings."
Think about it. When you measure and/or adjust toe, you are NOT moving the vehicle through any range of suspension travel.
All that being said, if a nearly level surface can be achieved in one's workshop without too much monkeying around, then one can have a superior space for ALL set up work.
I have clearly placed marks on my garage floor for set up work. They can be used with the tires directly on the floor, or they can be used with my scale roll-offs. Each roll-off has six adjustable feet, and I have those exact locations marked on my floor.
5-6 years ago I bought some roll-offs from a vendor on E-Bay... they are similar to Longacre Part #: 52-72905
http://www.longacreracing.com/produc...%22-scale-pads
(EDIT: Here is a link to what I bought: https://www.ebay.com/itm/Computersca...4AAMXQpwFRaHUY. I paid about $500 about 5-6 yeras ago).
I usually measure toe on my set up platforms because it is easier for me to reach underneath and make the adjustments without accidentally messing up my fishing lines (strings).
The ones I bought were about $500 or so. They work well with my scales, which are also Longacre units. I bought them used for about $500-- found in a local Craigslist ad years ago.
At one local shop, a set up on a trailing arm 911 can cost $500-1000--. As many know it can take many hours and many iterations to corner balance and align these cars.
I usually measure toe on my set up platforms because it is easier for me to reach underneath and make the adjustments without accidentally messing up my fishing lines (strings).
I am having a flashback... I remember when Craig first started selling SmartCamber (which came before SmartStrings) Two of my friends (both racers who run a high end racing data equipment company) bought a SmartCamber tool and decided to make their camber and caster measurements relative to the car at times when in a pinch. They are very accomplished and technical folks... they even have their own skidpad at their property.
Sorry, this is just not true. It isn't "necessary"-- repeatability can be achieved without a level surface.
Think about it.
Again:
"Doesn't toe change through the range of suspension travel? If so, having a non-level surface would impact the toe readings."
Think about it. When you measure and/or adjust toe, you are NOT moving the vehicle through any range of suspension travel.
All that being said, if a nearly level surface can be achieved in one's workshop without too much monkeying around, then one can have a superior space for ALL set up work.
I have clearly placed marks on my garage floor for set up work. They can be used with the tires directly on the floor, or they can be used with my scale roll-offs. Each roll-off has six adjustable feet, and I have those exact locations marked on my floor.
5-6 years ago I bought some roll-offs from a vendor on E-Bay... they are similar to Longacre Part #: 52-72905
http://www.longacreracing.com/produc...%22-scale-pads
(EDIT: Here is a link to what I bought: https://www.ebay.com/itm/Computersca...4AAMXQpwFRaHUY. I paid about $500 about 5-6 yeras ago).
I usually measure toe on my set up platforms because it is easier for me to reach underneath and make the adjustments without accidentally messing up my fishing lines (strings).
The ones I bought were about $500 or so. They work well with my scales, which are also Longacre units. I bought them used for about $500-- found in a local Craigslist ad years ago.
At one local shop, a set up on a trailing arm 911 can cost $500-1000--. As many know it can take many hours and many iterations to corner balance and align these cars.
I usually measure toe on my set up platforms because it is easier for me to reach underneath and make the adjustments without accidentally messing up my fishing lines (strings).
I am having a flashback... I remember when Craig first started selling SmartCamber (which came before SmartStrings) Two of my friends (both racers who run a high end racing data equipment company) bought a SmartCamber tool and decided to make their camber and caster measurements relative to the car at times when in a pinch. They are very accomplished and technical folks... they even have their own skidpad at their property.
Last edited by Mahler9th; 05-27-2020 at 01:51 AM.