UKC

Odd question, I know, but, this being UKC...

This is for a custom built, human powered vehicle that has been built around car hubs and currently has 105/70 R14 wheels on it - I think they are space-saver wheels from a VW Polo.

We are looking at putting a taller tyre on it to increase circumference and it occurred to me that fitting either a 100/90 R14 or 110/80 R14 motorbike tyre would both increase the circumference slightly and also lower the rolling resistance, due to the rounder profile.

Anyone tried doing this? I don't know enough about the differences between car and motorbike tyre beads to know if it would work.

Thanks,

Custom bike builders forums might be your answer. If you can resolve the necessary engineering, bike wheels would be better and be much lighter.

All those seem to talk about very wide rear tyres on custom choppers, as far as I can tell, which is way off what we need.

Apart from anything else, we don't have time to start hacking about with the chassis to change hubs and wheels

it has been known in less developed nations (cough... ahem... USA), to put car tiers on the back wheel of a motorbike.

the bead shapes are subtly different, but by extension of the above, if you can fit a tire it should be made possible. certainly for a low-load application.

I'll leave it to you to get the right tire (b.t.w motorbike tires are expensive)...........and, let's not re invent the wheel

The bead hump on a car rim is 21mm inwards, a motorcycle rim it's 16mm so a motorcycle tyre will fit in the bead groove of a car rim, not the other way round. I doubt your cornering forces will be of concern!

A heavy duty tube (3 or 4mm) will help even if the tyre is tubeless and as much air pressure as you dare! Balance the wheels really well and wash the wheel bearing grease out and use sewing machine oil.

New ones are. 

Second-hand tyres that are no longer road legal (fitted to a motorbike) should be blaggable for free though, from somewhere, and unless they've been deliberately destroyed in a 'burnout' would still be good enough for a human-powered vehicle.  It'd mostly be a question of asking the right person on the right day.  Though it might be an additional challenge to find a matching set for a vehicle that needs 3 or 4 of them.

A 14" 'er will be a scooter tyre so around £40 or so for something good like a Michelin Pilot which is about the most treadless you'll find (slicks are hard to find in 14"). Used tyres are mostly worn in the middle so not so good but some brutality with and angle grinder works wonders!

Thanks, that's exactly the answer I was hoping for.

Cruising speed on the flat is going to be under 10mph, I think - cornering forces not a concern.

Weight was my other concern - about 650kg over 4 wheels, but should be ok

The typical load range I looked at is 40P to 49P so 140kg to 185kg (front and rear tyres) and that's measured for sustained full speed not 10km/h! Pressure wise you should be o.k up to 8bar or so at a guess, takes a lot to actually explode the tyre especially with a tube in it. Another trick for less rolling resistance is spray the tyre with a silicone based lube and let it dry, lasts maybe 4 laps on supermoto training  bikes so should hold a while for you.

I'd inflate then spinning the wheel as fast as possible carve the contact patch down to maybe 10mm wide with an angle grinder, it's a bit of a dirty job!

I hope you will post a picture of the finished  'vehicle'.

HPV on car wheels?!

For cos I'd just try one or two, ebay them if the experiment fails. I'm interested in the outcome, I've been fancying a scaled down ultralight interwar style e-car build but under quad-bike reg's in order to run scooter tyres and dodge some other annoying car IVA stipulations. They're the right size, look, weight, jury is out on the lateral stiffness!.

Not sure Crr will actually be lower than for a space saver, with the small round contact patch there'll be more deformation all other things being equal.

jk

How many humans are powering this thing...?

That should read 'for the cost'

Grab some 16" scooter wheels and some sidecar tyres like the Haidenau K29, people with outfits have central wear and lateral stability issues as well! The MOT will probably accept them as well (they only accept car tyres on car rims so probably not motorcyle tyres on car rims.

Good tip on the sidecar wheels.

To hit my ridiculous weight requirements (driven by the very low 15kW max wheel power limit for a heavy quadricycle) and to get the 2/3rds scale look right I'd have to stick with very small scooter tyres (~14") and ultra lightweight custom wheels. I'd expect to have to make composite wheels and if so I'd probably splash a rim mould off an alloy scooter wheel then make my own hollow/sandwich centre. Definitely one to talk through with an MSVA inspector before going too far, an electric FRP monocoque homage to 30s Italian coachbuilding registered as a quad-bike would raise some eyebrows at the test centre whatever it was rolling on. I'm currently far from certain I can hit the weight/performance goals let alone the regulatory requirements but it's a slowburn idea I'll chip away at or abandon eventually.

jk

Cool by electric things (well scooters etc) the real power and rated power are completely different, I've had a spin on the BMW CE04 which is officially 14.7kW (20hp) but actually churns out 42hp.

14" you are also in the world of pit bike wheels, I've one somewhere I can weigh to see what your complete hub/wheel has to compete with.

Can't help, but I'm really curious about what you're building here!

How does that work a 42whp car makes 42whp when you dyno it which is definitely more than 20! Is output power averaged over a significant chunk of time allowing high peak power sprints but then cutting back well below 15kW after a few seconds? That would have little negative impact on city driving or a back-lane thrash where you're on the throttle-brakes-throttle constantly. MSVA rules simply say <15kW nett (presumably meaning wheel power), no mention of a test methodology.

The CE 04 has a maximum power of 31 kW (continuous power 15 kW), which should enable the “traffic light start” from 0 to 50 km/h in 2.6 seconds. BMW also offers a reduced-power version for the L3e-A1 vehicle class, which has a maximum output of 23 kW (continuous output 11 kW).

Apparently just that, I had no idea one could get away with bending the rules so far they no longer make any sense! Not sure I'd fancy my chances defending it in a court based on the MSVA rules without BMW's legal and technical firepower or a clear test method statement.

Oh, please.

jk

It's some the continous rating system for electric motors which keeps them within the permitted insulation temperature rise, there are different classes for different insulation materials or cooling.

It's a hot! issue at the moment in the motorcycle world particularly regarding the A1 class small motorcycles for young riders, the old 80km/hr limit was changed to 11kw but the electric ones are now appearing capable of ca 140km/hr and shocking acceleration, the BMW restricted version still has 62Nm as well as 31hp, only it's gargantuan weight slows it down (and it's regulated down to 120km/hr). The more normal sized 120kg-140kg things are crazy really. It's a bit like allowing learner bikes to be fitted with NOx. The EU are looking into it!

I'll dig the wheel out tomorrow, it's in a single-wheel offroad motorbike trailer at the moment (I make a few a year for a guy in Denmark). They are pretty good for the price (under €30) with alloy hub and rim, you could save some weight by changing the spoke nipples to alloy and maching the hubs because they come for both a sprocket and a disc brake. I'll look what bearings are available as a 12mm axle wouldn't cut it as a stub axle, the cycle car guys go to go-kart stuff.

Diff and rear axle it's off to the world of quads! Or rigid driving both wheels or one-wheel drive.

Beer time!

Maybe they got advice from VW...

I have some motorbike wheels and tyres you could have for that sort of project. Wrong diameter for you current rims though

So like E-bikes then where the regulations relate specifically and bizarrely to the motor power rating, an almost complete irrelevance when hooked to an electronic speed control where any power limits are actually imposed. Many electric motors will stand *massive* transient 'overloads', the diy EV builders often run theirs an order of magnitude or more over their ratings, the interesting question then becomes what constitutes transient given how most vehicles are used.

I don't really understand how that's come about, surely someone with some technical nous scrutinises these laws. To my mind if it peaks at 31bhp on a dyno it's 31bhp, that's what it would be rated were it IC even if that peak were unusably narrow from a screaming 2-stroke. As is with electric drive they'll have pretty flat power curves and remarkable performance vs 'like for like' power IC even without cheating.

A real world speed and peak acceleration limit seems the most robust way to legislate for these things but what do I know, someone would find a way to subvert it.

Yeah, lots of options to lighten and strengthen them to suit I'm sure. The cycle-cart racing guys inthe US planted the idea but with nowhere to race I'd build for the road.

Dual motor, chains, single sided trailing arms: I've been through a few iterations and can't find a lighter combination plus I have the motors (DC Agni/LEM pancakes).

jk

Here e-bikes are just limited to 25km/hr, don't know if there's a power limit at all.

The rating system for electric motors starts at if I remember correctly the insulation has to hold up for 20, 000hrs continous load, not suprisingly they take a bit of overload. Especially with some intelligent design using the transmission and chassis as a cooling system. I guess the actual rules were a rush jobby and now there's some rethinking going on.

Conventional motorbikes there's a limitation on what you can do, you can de-rate a larger bike to fit a lower category but the rules stop one producing a completely stupid torque monster by limiting the power of the original bike, restricting a Hayabusa isn't allowed! All kinda flexible though, my 450KTM is rated at 13kw to keep inside the power to weight ratio limit, still pulls 53 hp at the rear wheel though.

Going to be interesting synchronising two motors in a straight line, even more exciting telling them what to do in a corner!

UK e-bike legislation never quite lined up with EU and it's an unhelpful mess IMO.

I'm still scratching my head, is that 13kW average across the engine speed range? 53hp is nothing like 13kW, obviously!

Should be ok, I know of someone who built a Mini a with similar set-up in the front (2x 7" series-wound forklift motors IIRC, pretty torquey). DC motors linked in series operate like an open diff, when one wheel spins up it's BEMF climbs reducing the current to and torque from both, they produce matched torque for a matched pair. Linked in parallel they operate more like an LSD, when one spins up the other receives more current (for a given current input to the pair). With independent control you have options which is what I'll probably do since I'm not sure I'll have the headroom to run them to full speed in series. Given the low track-wheelbase ratio design and pretty modest output I suspect it's largely moot, they're unlikely to spin wheels in the dry at least and should provide little input to steering forces so long as the front geometry isn't too bonkers.

jk

Just normal manufacturer creativity, KTM probably just put a washer in the inlet tract to get the power to weight ratio correct for the holomogation then delivered the washer as part of a service prep kit to the dealer.

Weighed the wheel, 3.84kg with tyre. 38 x 12 x 12 wheel bearings so should be able to find something bigger.

Cheers

For a comparison as I had it on the workbench changing the disc a 125 Kawasaki 21" front with tyre but no brake disc is 6.6kg.

Apparently the rule is measured sustained power over 30 minutes.

The record at the moment is the E Choppers SR which has a rated 15hp and a peak of 59hp, along with 109Nm torque.

For pedal assisted "bicycles" one goes for the e-Rockit, 6.8hp to 21.7hp!