b'TECH TIP PAGETech Tip 65: For decades engineers couldnt explain why a percentage of tire load (andtherefore grip) was lost during body roll. Engineers just accepted that a percentage of loadtransfer on the tiresside to side, front to rear or any combinationwould be lost. Could be anywhere from 5-10% load loss. Meaning we werent loading the tires 100%. Lost grip.When Racers & Engineers started using 7-post shaker rigs to test suspension loading, everything came to light. Regular sprung race cars (no coil-bind or bump stops) showed theload transfer loss we came to accept. When they tested race cars utilizing coil-bind strategies,where the spring is completely collapsed & basically solid steel, the load transfer (grip) jumpedup to 99.8%. Almost 100%. The .2% is suspension flex. We now know that lost percentage of load transfer is due to energy loss through the spring wire. Upon testing more race cars on the 7-post with regular setups (not coil-bind or bump stop) testing showed the length of the wire that makes up the coil spring affects the net load & gripresult. The longer the wire is in a spring, the more energy loss, and load loss, there is. Lessgrip. Conversely, the shorter the wire is in a spring, the less energy loss, and load loss, there is.Since then, spring companies now make coil springs with less wire. A 12 x 2.5 ID 500# coil- over spring from 25 years ago had 10-11 coils. Today, race spring companies make that same 12 x 2.5 ID 500# coil-over spring with 7-8 coils. You can see the larger spacing betweencoils. Veteran racers can feel more grip & the stop watch shows measurably faster lap times.This requires higher grade spring wire & better spring manufacturing processes. So today, werun the shortest wire spring we can that achieves our rate & target amount of travel.Back on the 7-post shaker rigs, Race Engineers learned about tire loading with bump stops. The key take away is bump stops are almost as efficient as coil-bind. Almost. Plus, they areless expensive, more forgiving on track, easily tunable & provide good feedback to the driver.This is good, since 90% of race drivers, crew chiefs & team owners hate coil-bind strategies.Coil-bind springs are $2000 each. They have to stack within .020 precision or you haveproblems. If you change your setup slightly, you have to buy new springs. They feel horrible inthe car, since the suspension is basically solid metal. The only give is the tire sidewall. Bump stops come in a wide range of hardnesses & spring rates. The harder the bump stop is, the quicker the rate comes up & the more efficient it is (less load & grip loss). But it is lessforgiving in the car. The rate comes up slower in softer bump stops, so the feel improves & thecar is more forgiving. But we lose some efficiency & experience more load & grip loss.In sportsman racing, we run the stiffest bump stop the track & driver will tolerate. In pro racingwe ignore the drivers complaints of harshness. On smooth tracks, we run the stiffest bumpstops, have the highest grip & run faster lap times. Rougher tracks require us to back off to softer bump stops. Otherwise, the front end will skip over the undulations in the track surface.We want to be as aggressive with bump stop rate as we can, without upsetting the car.1094'