tire size and gear effects on dyno numbers?
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From: Houston, tx
tire size and gear effects on dyno numbers?
Im curious about the effects of tire size, gear ratios, tire pressures, etc. on dyno numbers.
The last dyno I had, after adding 4.10s, showed a really big HP loss... something like 10% or more.
The dyno operator insisted that an increase from 3.73s to 4.10s accounted for the difference.
Since increasing or decreasing tire diamter will have basically the same effect as slight gearing changes, I'm curious how this affects the final numbers.
I noticed when setting up the dyno, he chose a vehicle from the list. Does the dynojet computer system have to be told what the tire size is, the gear size, etc. to get accurate results? If so, wouldn't it have made sense for him to "change" a parameter or two? (he didn't as far as I could tell).
So lets say I go to the dyno and I have a tire that is about 5% larger (OD) than stock. I still have the 3.73s, but what does this larger tire do to my numbers. If I did a back to back with stock sized tires and these, what would the HP difference be, if any? If I do back to back dyno runs with 3.73s and 4.10s, what will the results look like?
I'm really interested in what would happen, but more importantly *why* and *what*, if anything, can be done to be sure one dyno to the next is accurate.
The last dyno I had, after adding 4.10s, showed a really big HP loss... something like 10% or more.
The dyno operator insisted that an increase from 3.73s to 4.10s accounted for the difference.
Since increasing or decreasing tire diamter will have basically the same effect as slight gearing changes, I'm curious how this affects the final numbers.
I noticed when setting up the dyno, he chose a vehicle from the list. Does the dynojet computer system have to be told what the tire size is, the gear size, etc. to get accurate results? If so, wouldn't it have made sense for him to "change" a parameter or two? (he didn't as far as I could tell).
So lets say I go to the dyno and I have a tire that is about 5% larger (OD) than stock. I still have the 3.73s, but what does this larger tire do to my numbers. If I did a back to back with stock sized tires and these, what would the HP difference be, if any? If I do back to back dyno runs with 3.73s and 4.10s, what will the results look like?
I'm really interested in what would happen, but more importantly *why* and *what*, if anything, can be done to be sure one dyno to the next is accurate.
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Joined: Oct 2002
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From: Central Joisey
Tire size affected my dyno results. I noticed at the track I was running slower (ET and MPH) with 26" tall tires. While I was at the dyno I did 3 pulls with 26" tall tires and 3 pulls with 28" tall tires.
Sorry about the sideways images. Run 10 is with 26" tall ET Streets and Run 7 is with 28" tall F1's. Pretty big loss for me. Of course different combinations would react differently to gear ratio changes. My opinion is that 3:73's and 28" tall tires are on the limit of optimum.
Edit: Sorry I screwed up, run 7 was with 28", run 10 was with 26" tall tires.
Sorry about the sideways images. Run 10 is with 26" tall ET Streets and Run 7 is with 28" tall F1's. Pretty big loss for me. Of course different combinations would react differently to gear ratio changes. My opinion is that 3:73's and 28" tall tires are on the limit of optimum.
Edit: Sorry I screwed up, run 7 was with 28", run 10 was with 26" tall tires.
Last edited by yysenhimer; Nov 19, 2003 at 07:20 PM.
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From: Cave Creek, AZ
Ken,
He chose a vehicle from a list because that's where the run is stored. When you set the car up on the dyno you need to tell the software where to store the run information. He was probably picking something like the Ford/F-150 directory or something for your dyno files. Outside of that and a few other small parameters (A/F on or off, etc.) there isn't anything else to set up on the dyno that would tell it car specific information like gear ratios or anything.
Dan
He chose a vehicle from a list because that's where the run is stored. When you set the car up on the dyno you need to tell the software where to store the run information. He was probably picking something like the Ford/F-150 directory or something for your dyno files. Outside of that and a few other small parameters (A/F on or off, etc.) there isn't anything else to set up on the dyno that would tell it car specific information like gear ratios or anything.
Dan
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From: Houston, tx
Originally posted by Calightnin
Why do you think gear ratio, or tire size would produce different peak HP/TQ numbers?
Why do you think gear ratio, or tire size would produce different peak HP/TQ numbers?
That's not within the margin of error...
The truck was running as strong as ever. The butt dyno would have noticed a 40HP loss.