Equating Un-Sprung Mass Reduction to Wheel BHP
Discussion
The following quote from a manufacturer of lightweight wheels got me thinking......
"The performance gain achieved by reducing the wheel mass (Un-sprung Mass) can be quantified using a factor of six. This means that to achieve the same performance gain by reducing the body mass, it is necessary to remove six times the wheel weight saving.
Example A saving of 2Kg Per Wheel x 4 Wheels = Removing 48 Kg from the Bodywork."
......how much extra power at the wheels would you need to get the same improvement in performance that reducing the un-sprung weight brings - is there a formula out there equating the two or even a simple "rule of thumb" ?
"The performance gain achieved by reducing the wheel mass (Un-sprung Mass) can be quantified using a factor of six. This means that to achieve the same performance gain by reducing the body mass, it is necessary to remove six times the wheel weight saving.
Example A saving of 2Kg Per Wheel x 4 Wheels = Removing 48 Kg from the Bodywork."
......how much extra power at the wheels would you need to get the same improvement in performance that reducing the un-sprung weight brings - is there a formula out there equating the two or even a simple "rule of thumb" ?
...In fact it's a bit weasley-worded altogether. I imagine they're trying to claim that it will improve acceleration time 6 times better than removing that amount of mass from elsewhere on the car. While I guess that's possible in some circumstances, I'd be deeply sceptical that it would be true for EVERY car! Clearly it wouldn't do much for "top end" performance, and neither would removing weight from elsewhere in the car. For acceleration it's the moment of inertia of the wheels that would make the biggest difference. That's related to mass but the distribution of that mass (closer to the centre or nearer the rim) makes a big difference too. Ask them if it goes even better if you buy a spare wheel off them too!
I'm not actually buying the wheels as I have already replaced my spiders. My angle is that for someone who is looking to increase accelerative performance would it be better to change the wheels to reduce mass or say have an engine re-map to free up some extra BHP. The question then becomes how much power would you need to free up as part of the re-map to make it a better option than changing the wheels ?.
Recently I replaced my wheels with lighter ones.
The immediate effect was a big increase in ride comfort. I have stiffer springs and Nitrons, all well set up for handling. But it was a bit inclined to crash and jar over poor road surfaces.
Weather conditions and trying to cure new tyres in freezing slippery conditions have prevented me testing properly and setting it up again yet.
However, my impressions are that the wheels are now more likely to be in contact with the road. It feels much less likely to be destabilised by mid-bend bumps. On a track it might pay me to stiffen it up again, but for road conditions, it feels quicker now than it did.
The immediate effect was a big increase in ride comfort. I have stiffer springs and Nitrons, all well set up for handling. But it was a bit inclined to crash and jar over poor road surfaces.
Weather conditions and trying to cure new tyres in freezing slippery conditions have prevented me testing properly and setting it up again yet.
However, my impressions are that the wheels are now more likely to be in contact with the road. It feels much less likely to be destabilised by mid-bend bumps. On a track it might pay me to stiffen it up again, but for road conditions, it feels quicker now than it did.
One of the factors to consider with lightweight wheels is how strong they are. I use the standard 16" Imola wheels, which are pretty heavy but very tough. I've only bent one once, and that was dropping the outer rear into a huge pothole while powering out of a corner so most of the weight of the car was on it. The impact was huge and I honestly thought I was going to lose the whole wheel, but it just had a slight flat spot that Pristine straightened out for me. Other times I thump the curbs pretty hard and generally just take it for granted that the wheels will stand it OK because I know now how tough they are. With lighter more delicate wheels you wouldn't be able to take that for granted.
Have you guys actually weighed your "lighter" wheels?
I have a set of Team Dynamics 17" rims with Toyo proxes and a set it Factory Esterils with R888's on...I was asked one day why I had the track day tyres on the heavier wheels? which was a simple answer as I could not get road tyres in the right speed rating for the 15" fronts so I Bought the 17" rims for that reason. Later on I decided to reuse the Esterils for trackays with the R888's.
Having been asked the question, I got me to thinking
how much heavier are the std tvr wheels? well, would it surprise you to know that that my R888 shod 15" Esterill is actually !kg lighter than than the 17" light weight shod with Proxes?
the rears work out the other way around by !kg, but the fronts were a surprise to me.
I have a set of Team Dynamics 17" rims with Toyo proxes and a set it Factory Esterils with R888's on...I was asked one day why I had the track day tyres on the heavier wheels? which was a simple answer as I could not get road tyres in the right speed rating for the 15" fronts so I Bought the 17" rims for that reason. Later on I decided to reuse the Esterils for trackays with the R888's.
Having been asked the question, I got me to thinking
how much heavier are the std tvr wheels? well, would it surprise you to know that that my R888 shod 15" Esterill is actually !kg lighter than than the 17" light weight shod with Proxes?the rears work out the other way around by !kg, but the fronts were a surprise to me.
Bluebottle said:
Have you guys actually weighed your "lighter" wheels?
I have a set of Team Dynamics 17" rims with Toyo proxes and a set it Factory Esterils with R888's on...I was asked one day why I had the track day tyres on the heavier wheels? which was a simple answer as I could not get road tyres in the right speed rating for the 15" fronts so I Bought the 17" rims for that reason. Later on I decided to reuse the Esterils for trackays with the R888's.
Having been asked the question, I got me to thinking how much heavier are the std tvr wheels? well, would it surprise you to know that that my R888 shod 15" Esterill is actually !kg lighter than than the 17" light weight shod with Proxes?
the rears work out the other way around by !kg, but the fronts were a surprise to me.
I was looking at lightweight wheels today and it seems to increase 1kg for every inch larger you go, as a rule of thumb of course and going from 15 to 17 you gain a little in width too,I have a set of Team Dynamics 17" rims with Toyo proxes and a set it Factory Esterils with R888's on...I was asked one day why I had the track day tyres on the heavier wheels? which was a simple answer as I could not get road tyres in the right speed rating for the 15" fronts so I Bought the 17" rims for that reason. Later on I decided to reuse the Esterils for trackays with the R888's.
Having been asked the question, I got me to thinking
how much heavier are the std tvr wheels? well, would it surprise you to know that that my R888 shod 15" Esterill is actually !kg lighter than than the 17" light weight shod with Proxes?the rears work out the other way around by !kg, but the fronts were a surprise to me.
on the theme of unsprung weight saving is there much to gain in changing standard granada brakes for the later tvr brakes or wilwood brakes, also i read somewhere that turning the shocks upside down so the spring was at the bottom also has an effect on unsprung weight and responsiveness.
You don’t say which Team Dynamics wheel, or rim width you fitted, but I fitted Pro Race 1.2 in 17” all round.
After much consideration, I kept the rim width as small as possible for the tyres I wanted to fit. A lot of people seem to just buy as wide a wheel as they can. If they fit an unnecessarily wide wheel then it is just extra weight without benefit. I opted for 7.5 with 215 and 8 with 245 tyres.
The original Estorils were fitted with almost worn out Proxy TS1 and SO2. The new 17” came with new Proxy TR1.
The new wheels were lighter, but I didn’t measure the difference. In changing the wheels I had the old in one hand and the new in the other. The difference in weight was very noticeable. I swapped hands to make sure I wasn’t imagining it, but there was still an appreciable difference.
After much consideration, I kept the rim width as small as possible for the tyres I wanted to fit. A lot of people seem to just buy as wide a wheel as they can. If they fit an unnecessarily wide wheel then it is just extra weight without benefit. I opted for 7.5 with 215 and 8 with 245 tyres.
The original Estorils were fitted with almost worn out Proxy TS1 and SO2. The new 17” came with new Proxy TR1.
The new wheels were lighter, but I didn’t measure the difference. In changing the wheels I had the old in one hand and the new in the other. The difference in weight was very noticeable. I swapped hands to make sure I wasn’t imagining it, but there was still an appreciable difference.
s5tvr said:
slideways said:
also i read somewhere that turning the shocks upside down so the spring was at the bottom also has an effect on unsprung weight and responsiveness.
Interesting - Joolz any thoughts on this ???Avocet said:
s5tvr said:
slideways said:
also i read somewhere that turning the shocks upside down so the spring was at the bottom also has an effect on unsprung weight and responsiveness.
Interesting - Joolz any thoughts on this ???http://www.pistonheads.com/GASSING/topic.asp?h=0&a...
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