Top speed and weight

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MartinClan
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Top speed and weight

Post by MartinClan » Fri Dec 02, 2016 9:37 am

I have almost completed th MSVA form. I am not sure what to enter for the top speed and weight.

Calculated top speed (guzzi engine and 19" skinny wheels) is 90mph. Guestimate of weight 350kgs. Are those figures OK?

Cheers Robin
Robin Martin
#335 Silvermachine
Small block 750 Moto Guzzi

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davidtocher
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Re: Top speed and weight

Post by davidtocher » Fri Dec 02, 2016 9:47 am

The weight is used for the braking test but I recall the examiner saying it doesn't matter cos he weighed each wheel when testing the brake efficiency. The max speed must be less than the tyre speed rating. This is marked on the tyre with some code. I think the speedo has to cover the declared max speed.

The registration folk need the weight to decide which class the vehicle is assigned. I think 410kg is the max for our sort of trike. I got a weight bridge cert from the local council recycling centre.
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MikeM
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Re: Top speed and weight

Post by MikeM » Fri Dec 02, 2016 3:12 pm

Robin,
Vintage Tyres have tyre data on their site. As David T says, state a max speed inside the rating for the tyre - also tie it in with the stated max rpm for the motor. Like the Guzzi, the BMW will rev out to 7,000 if pressed, but I played the mechanical sympathy card (30+ year old, rebuilt motor/ want it to last....) and opted for 6,000 max rpm. With gearing around the 14mph per 1,000rpm in 4th (with 19" wheels your gearing will likely be longer, but I'd stay away from that) that allows for a top sped of say 85mph. It also has a bearing on the revs the tester will ask you to hold, for the noise test, being a percentage of max revs as stated.

You probably had all of this with the Marlin!
It's a 2CV Jim, but not as we know it.

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Re: Top speed and weight

Post by Colin-gser » Sun Dec 04, 2016 8:31 pm

Hi

I thought pg listed weights in the build manual, if not he should be able to advise - you don't want to be too far out when tester weighs car

90 sounds a sensible top speed, this is probably asked mainly to check tyre speed rating surely rather than for any other purpose so make sure you don't shoot yourself in the foot!

Colin
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MartinClan
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Re: Top speed and weight

Post by MartinClan » Mon Dec 05, 2016 8:23 am

Thanks all. I checked the Avons I am using and they have a speed rating of S which I think is good for 120mph - so my calculated top speed of 90 should be fine.

I didn't realise the weight was in the manual (I haven't looked at it much recently) so I'll check there.

Cheers, Robin
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Re: Top speed and weight

Post by Colin-gser » Fri Jan 13, 2017 6:39 pm

Hi

As stated weight in the manual

As far as top speed concerned if a 2cv engine just quote top speed for that - same gearing so top speed the same, if guzzi engine you're presumably still controlled by gearing

They won't be testing it!

Colin
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duncan grimmond
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Re: Top speed and weight

Post by duncan grimmond » Fri Jan 27, 2017 8:29 am

I would recommend visiting your local weighbridge. There will be a Local Authority one somewhere or if not, the local scrap/metal recycler will have one accurate to 10kg.
As little fuel as possible, no spare wheel, no toolbox etc. This will give you a pointer to avoid any problem of being overweight for your category.
Be sure to get your max HP/ r.p.m into the right end of the cut-off point, just in case your exhaust is a bit noisier at high revs.

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Re: Top speed and weight

Post by Tom Rae » Fri Jan 27, 2017 9:44 am

duncan grimmond wrote:I would recommend visiting your local weighbridge. There will be a Local Authority one somewhere or if not, the local scrap/metal recycler will have one accurate to 10kg.
As little fuel as possible, no spare wheel, no toolbox etc. This will give you a pointer to avoid any problem of being overweight for your category.
Be sure to get your max HP/ r.p.m into the right end of the cut-off point, just in case your exhaust is a bit noisier at high revs.
Duncan whilst I appreciate your reasoning, it is often very difficult to do this with an unregistered car, I gave up! It is important to consider weight during your three wheeler build and nought wrong with bathroom scales under each wheel in turn?

Tom
Chassis # 181 "Snotamog"
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750 Guzzi

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duncan grimmond
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Re: Top speed and weight

Post by duncan grimmond » Fri Jan 27, 2017 10:31 am

I agree it's not essential and, you can weigh the car with bathroom scales but we don't seem to have any!
Taking an unregistered car to a weighbridge is surely no more difficult than taking it to the VOSA centre unless it's miles away? I insured the cars on chassis number and drove for a booked pre-test MoT (not to be entered on the computerised system) using the donor number and called in at the weigh bridge on the way. I took the cars, 60miles each way, to VOSA on a trailer.
I'm lucky in that the weighbridge is only 5 miles away so I did this to save any possible embarrassment at the test. As it turned out I was well within the weight limits.

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Re: Top speed and weight

Post by Tom Rae » Fri Jan 27, 2017 11:21 am

duncan grimmond wrote:I agree it's not essential and, you can weigh the car with bathroom scales but we don't seem to have any!
Taking an unregistered car to a weighbridge is surely no more difficult than taking it to the VOSA centre unless it's miles away? I insured the cars on chassis number and drove for a booked pre-test MoT (not to be entered on the computerised system) using the donor number and called in at the weigh bridge on the way. I took the cars, 60miles each way, to VOSA on a trailer.
I'm lucky in that the weighbridge is only 5 miles away so I did this to save any possible embarrassment at the test. As it turned out I was well within the weight limits.
Duncan, I am not convinced it is legal to drive to an unnecessary and unrecorded MOT and subsequent weighbridge despite it only being 5 miles away. Any accident would soon call into question your insurance too. In my view, both the weighing and pre mot are not necessary and the consequences should be carefully thought about before doing it.

Righteous perfect Tom
Chassis # 181 "Snotamog"
LWB Grasshopper SS
750 Guzzi

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