Tire diameter instead of diff gears?
Thread Starter
Teching In
Joined: Jul 2017
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Tire diameter instead of diff gears? Hey guys, first time poster long time listener, bit of a question for you.
I have a gtech pro, and use that as a baseline in my ls1/4l60e swapped corvette c3. Heads ported and mild cam, weighs about 2800-2900lbs, consistently have been getting the quarter mile in 12.1, and 0-60 in 3.7secs, the rear tyres are Hoosier dot radials (track oriented, not drag), they are 275/50/15, need to get some heat in them to grip, otherwise they are worse than street tires. So I upgraded to new Micky thompsons et street ss 255/60/15, grip way better, but now my et is around 12.6, 0-60 about 4.1. My rear end ratio is 2.87.
Have been comparing gtech results, and I would say that the smaller diameter of the Hoosiers is acting like smaller diff gears, and going off the speedo/rpms, I would say there is a 8% reduction in the final drive (8mph off at 100mph etc)
Would that explain it completely? Is that equivalent to a 8% reduction in diff gears? (Ie, going from 2.87 to 3.10)?, and if so, does going from such low gear to low gears in that example really reduce the et by half a second? I wouldn't think even going from 2.87 to a 4.11 would get even half that, let alone 2.87 to 3.10
Can anyone explain the consistently MUCH slower times due to only tyre change? The Hoosiers weigh in total 12lbs less, that would be a very slight part of it I guess too
I have a gtech pro, and use that as a baseline in my ls1/4l60e swapped corvette c3. Heads ported and mild cam, weighs about 2800-2900lbs, consistently have been getting the quarter mile in 12.1, and 0-60 in 3.7secs, the rear tyres are Hoosier dot radials (track oriented, not drag), they are 275/50/15, need to get some heat in them to grip, otherwise they are worse than street tires. So I upgraded to new Micky thompsons et street ss 255/60/15, grip way better, but now my et is around 12.6, 0-60 about 4.1. My rear end ratio is 2.87.
Have been comparing gtech results, and I would say that the smaller diameter of the Hoosiers is acting like smaller diff gears, and going off the speedo/rpms, I would say there is a 8% reduction in the final drive (8mph off at 100mph etc)
Would that explain it completely? Is that equivalent to a 8% reduction in diff gears? (Ie, going from 2.87 to 3.10)?, and if so, does going from such low gear to low gears in that example really reduce the et by half a second? I wouldn't think even going from 2.87 to a 4.11 would get even half that, let alone 2.87 to 3.10
Can anyone explain the consistently MUCH slower times due to only tyre change? The Hoosiers weigh in total 12lbs less, that would be a very slight part of it I guess too
Joined: Aug 2007
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From: Turnin' Wrenches Infractions: 005
What converter? Usually with properly setup combos and good converters you dont see much change with small gear or tire changes like you describe....but with small or stock converters i could see it effecting it more.
How much heavier were the mickeys?
I agree the gear change should have little effect.
A little tire slip however may be faster than a dead hook, especially with a taller tire, if the car doesn't have much power from a dig.
I agree the gear change should have little effect.
A little tire slip however may be faster than a dead hook, especially with a taller tire, if the car doesn't have much power from a dig.
Thread Starter
Teching In
Joined: Jul 2017
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Stock converter, 3500 coming this week, that will help a lot obviously.
each Hoosier is about 2.5-3lbs less (and closer to center of gravity) than Micky's. But half a second is a lot.
and the Hoosiers would dead hook if I feather the throttle for the first 3 or 4ft, where the Micky's can dead hook if I try flash or stall the (stock) converter, although 0.1 slower 60' with mickys, due to the dead hook and slight bog, but would say more to do with the ratio.
A better example is my gtech says that my pull in gear from 60-100 is about .35secs slower, and there isn't any variables like gear changes, wheel spin etc. so tire grip isn't the factor I would say
each Hoosier is about 2.5-3lbs less (and closer to center of gravity) than Micky's. But half a second is a lot.
and the Hoosiers would dead hook if I feather the throttle for the first 3 or 4ft, where the Micky's can dead hook if I try flash or stall the (stock) converter, although 0.1 slower 60' with mickys, due to the dead hook and slight bog, but would say more to do with the ratio.
A better example is my gtech says that my pull in gear from 60-100 is about .35secs slower, and there isn't any variables like gear changes, wheel spin etc. so tire grip isn't the factor I would say
It doesn't add up. You went .4 slower in the 60' and .35 slower from 60-100, that's .75 seconds slower but the 1/4 mile time was only .5 second slower.
I think the issue is more likely DA related. Temperature, barometric pressure, humidity even wind would make a larger difference than an 8% gear change.
I've gone from a 3.42 to a 4.10 and only picked up .2 seconds and 3.23 to a 4.30 and picked up .3 in a different vehicle.
I think the issue is more likely DA related. Temperature, barometric pressure, humidity even wind would make a larger difference than an 8% gear change.
I've gone from a 3.42 to a 4.10 and only picked up .2 seconds and 3.23 to a 4.30 and picked up .3 in a different vehicle.
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Agreed, to not put too much stock in the G-Tech numbers. 0-60 in 3.7 and a 12.1 1/4 mile don't match. Should probably be closer to 5 sec 0-60.
I did 0-60 in 3.8 and the 1/4 mile in 10.87 at the track with a soft 1.74 60'.
Al
I did 0-60 in 3.8 and the 1/4 mile in 10.87 at the track with a soft 1.74 60'.
Al
Thread Starter
Teching In
Joined: Jul 2017
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Yeah I am thinking it might be the gtech, although there were some aspects of the "new ratio" that gained a little advantage over the smaller tyres, it pulls 6 or 8mph longer in gear as opposed to shifting from 1st gear and then second stays in. Near redline nearly 12mph longer, so that would make up possibly a tenth or 2,
out of curiosity, what do a lot of you guys do 0-60? I would think low 3's are very achievable seeing as stock corvettes or newer muscle cars tend to go hard, but then all you blokes monster them in the 1/4 or to 100, I would think anyone running under 11.5 or so has a 0-60 of less than 3.5
out of curiosity, what do a lot of you guys do 0-60? I would think low 3's are very achievable seeing as stock corvettes or newer muscle cars tend to go hard, but then all you blokes monster them in the 1/4 or to 100, I would think anyone running under 11.5 or so has a 0-60 of less than 3.5
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the better gearing and lighter weight makes a heck of a difference. I always run the lightest wheels I can find (for economy, though). And being able to adjust the rear gearing slightly using tire size is icing on the cake.
Get everything dialed in together, though. Don't usually try to adjust or worry about tire size or weight until you have the suspension/converter/engine setup the way you want it first. If the goal is mph, example, you want to trap exactly 150mph. You would center in on going 151~mph in 1:1 without overdrive using an exact number gear in the rear with exact tire size, plus or minus any wear and deformations that change distance in a single revolution of a tire that isn't slipping.
Other times, the goal isn't mph. It might be mileage, longevity, power, burnouts, etc. if the goal was burnouts and never, ever mph caring, you could use a 6:1 or 10:1 or something nuts with a smaller engine to just get 5mph burnouts easily.
Get everything dialed in together, though. Don't usually try to adjust or worry about tire size or weight until you have the suspension/converter/engine setup the way you want it first. If the goal is mph, example, you want to trap exactly 150mph. You would center in on going 151~mph in 1:1 without overdrive using an exact number gear in the rear with exact tire size, plus or minus any wear and deformations that change distance in a single revolution of a tire that isn't slipping.
Other times, the goal isn't mph. It might be mileage, longevity, power, burnouts, etc. if the goal was burnouts and never, ever mph caring, you could use a 6:1 or 10:1 or something nuts with a smaller engine to just get 5mph burnouts easily.
Last edited by kingtal0n; Jul 23, 2017 at 11:11 PM.
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TECH Fanatic
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From: olympia, wash
I can offer this.
Just day before yesterday I went to a local tnt on my daily driver combo. It was a last minute thing.
My strip combo are 28x11.50 QTP's in the rear with hoosier front runner's on Weld 15" rts rim's. A pretty light combo.
150 shot jets in the plate.
My trap with the above combo is 126-127mph.
My street combo is 26" et street's, [bias] on stock rims, plate jetted down from 150 to only 100.
So 50 less hp.
My trap was 124.30mph.
only a couple mph slower with less hp and a much heavier wheel/tire combo.
My 60' was for ****, [1.88] but she was motoring pretty good.
Now I won't argue that the track conditions played a part.
But I do believe that xtra 2.2" of tire height played a good part.
Just day before yesterday I went to a local tnt on my daily driver combo. It was a last minute thing.
My strip combo are 28x11.50 QTP's in the rear with hoosier front runner's on Weld 15" rts rim's. A pretty light combo.
150 shot jets in the plate.
My trap with the above combo is 126-127mph.
My street combo is 26" et street's, [bias] on stock rims, plate jetted down from 150 to only 100.
So 50 less hp.
My trap was 124.30mph.
only a couple mph slower with less hp and a much heavier wheel/tire combo.
My 60' was for ****, [1.88] but she was motoring pretty good.
Now I won't argue that the track conditions played a part.
But I do believe that xtra 2.2" of tire height played a good part.