Tom@TPC Racing

Thank you to Leong72 and JD-Motorsports for posting your experience! Your method of measuring toe deviation is sound. Same with many race teams, of course we check bump steer the old fashioned way with wheel off, no spring, and use dial indicators or string & machinist's rule. But when applicable(race cars with 1000+lbs springs aren't applicable) we also back it up with laser alignment machine afterwards to verify consistency. On alignment machine, it is done with wheels, tires, and springs which IS how we drive the cars, to which I feel this method is more actual than the old fashioned mechanical simulation, as the suspension parts are loaded and unloaded closer to actual driving conditions. Not knocking on the old fashioned method at all, we still do those too. As long as the alignment machine heads/fixtures are calibrated and attached properly the results will be the same. As for your specific before/after results, in percentage of reduction, it is better than ours because your car is running more negative camber. We are right at 50% reduction, whereas yours is greater than 50%. Well done, guys!

On a completely separate note, just wanted to share the following- Last week I received a phone call from a former Penske Racing engineer who owns a GT4. He saw the TPC GT4 offset rear toe links in a print ad and felt compelled to call us. He stated his intention of the call clearly in saying that I am not calling you to buy set, because I have custom made a set already for my car after doing the development myself. He came up with the same positive results as we did. He just called to give us his nod of approval for the idea and the product. For what little that's worth to everyone else, I felt honored that he took the time to call.

TM5

Tom - pardon me if this has already been answered - but can you confirm your offset rear links are compatible with a 19 inch wheel set up? Thank you

Tom@TPC Racing

No worries. Yes they will clear true 19" wheels. When I say true I mean the inside diameter of the wheel barrel was designed originally as 19's. Some wheel companies actual use 18" inner barrels and build the lip area up to 19". Obviously this 18/19" hybrid type wheels won't clear.

Eric5280

Tom, my understanding is the GT4 cannot clear any 18" barrels. Can you give advice on how we can tell if we have a "true" 19"? OZ Leggera HLT in this case. Thanks.

Tom@TPC Racing

Sorry, I should have phrased it differently. If the wheel in question clears the OEM rear toe link then it will clear TPC rear toe link as well. The TPC links is actually 2mm shallower than OEM at where the wheel barrel over laps.

Eric5280

Perfect, thank you!

Mech33

Alright I may just have to give these TPC toe links a try on my GT4... TPC and all the other shops chiming into this thread seem like class acts that really know their stuff.

PLC

Well, I guess I'm a little late to the party. I took measurements as promised, but haven't had a chance to do anything until this week. Sure enough, with rough GT4 dimensions, the effect of the offset bushing in my simulation is significantly larger. You can see that the TPC-style offset bushing has ~40% less toe change across the entire range of travel. For reference, I measured about 1/4" of offset on a TPC piece.



Sadly, no Faro Arm or similar was involved in my measurements. Small tweaks in the position of hardpoints in my ADAMS model show quite a large effect on the toe curve, so I wouldn't be inclined to rely on this for more than order of magnitude. Fortunately, there's plenty of on-vehicle test data to prove my original result wrong! So a very strong thank you to Leong72 for posting that.

Phokaioglaukos

PLC, must be a bummer having a day job....

Thanks for the analysis!

Mech33

Glad to see the analysis roughly lines up with the empirical data. Thanks for taking the time to pull this analysis together and present the data so clearly!